1. Field of the Invention
The invention relates to a mould for producing a tooth model from a dental impression.
2. Background Art
Such moulds are known in the form of cup-shaped formed bodies.
To produce a tooth model from a dental impression, the dental impression is filled with a plastic modelling material which hardens. Immediately after filling the dental impression with the modelling material in rare cases, while the modelling material is still soft, a mostly rubber-like mould is applied to the peripheral wall of the dental impression in order, by filling the mould up to a predetermined height, to obtain a base on the tooth model.
To produce artificial teeth, said base is trimmed parallel to the occlusal plane mechanically by grinding; the result is a so-called toothed rim made of modelling material.
Then a drill and a twist drill are used to drill blind holes in the base of the toothed rim, in each case under the teeth to be restored, adjacent teeth or antagonists, and metal pins are introduced and preferably glued into the blind holes.
After subsequent isolation of the base mostly using an alginate-based isolating material, the toothed rim with the glued-in pins is basally aligned and introduced into a mould, which is filled to a height of around two centimeters with preferably the same plastic modelling compound, until the base of the toothed rim is just completely wetted by the plastic modelling compound. Said compound after it has hardened forms the base for the toothed rim; toothed rim and base together form the finished tooth model.
After hardening and mechanical trimming of the base, the toothed rim is sawn in each case at right angles to the tangent predefined by the individual tooth groups right down to the base such that the model teeth to be restored, neighbouring teeth, maxillomandibular segments or any other model teeth or model tooth groups may be individually removed from the base and precisely repositioned by means of the pins.
Such a saw-cut model is a prerequisite for producing any type of artificial tooth from dental impressions.
Another way of producing model bases is such that the parallel-trimmed, conventionally produced toothed rims are provided in a special drilling apparatus with the blind holes for the pins and at the same time mirror-image holes are drilled into a prefabricated base plate made of plastic material for receiving the pins, which are to be glued into the toothed rim, together with the toothed rim. Removal of the prepared teeth is effected by the conventional saw-cut technique. Although this dispenses with the outlay for processing a second plastic modelling compound for producing the base, expensive equipment is necessary.
A particular problem associated with producing tooth models, in particular toothed rims, is the filling of the mostly hydrophobic dental impression with the hydrophilic modelling material, usually dental plaster. The narrow indentations of the individually moulded teeth, undercuts occasioned by the tooth shape and fine delineation of the textured surface of the teeth in most cases promote bubble formation in the tooth model which often makes it necessary to produce a second tooth model. Such a second tooth model however is mostly of an inferior quality to the first tooth model because the removal of the latter from the dental impression simultaneously leads to the breaking-off of fine edges and surface structures as well as fine interdental lamellae or lamellae in the sulcus region.
In addition, defects attributable to the shaping by the dentist to obtain the dental impression are frequently only detectable on the tooth model. Because of the elaborate process of producing the latter, however, defects are mostly not spotted until several days after taking the impression from the patient. In many cases the patient has to be brought back for a new impression to be taken, which entails a high outlay and often leads to poorer impression results because a common consequence of the initial treatment is a tendency to bleed during the follow-up treatment.